Microdevices having bonded conductive and insulating substrates can be fabricated with many different materials. A combination of metal, glass, and semiconductor materials are often used to create these devices and their packages. These materials are fused into a structure by many different processes as are known in the art. Some of these devices require a sealed chamber with a device therein and electrical connections to outside the package. There are very many microdevices that typically have a requirement for this type of structure. Considering the variety of devices, one feature many of these devices have in common is complex structures that must be contained in separate hermetic packaging, which can be difficult to manufacture and expensive to produce. In addition to packaging issues, there are operational issues.
For example, microdevices manufactured by MEMS technology are playing key roles in many areas. For instance, micromechanical gyroscopes have enabled several important control systems in transportation and commercial applications. Other microdevices such as pressure sensors, accelerometers, actuators and resonators fabricated by MEMS technology are also used in many areas. Some microdevices, such as micro gyroscopes and resonators contain a microstructure that not only needs to be hermetically sealed but also needs to be maintained within a vacuum-sealed cavity. For these types of devices, there is a continuing need to provide a vacuum environment and to improve the longevity of the vacuum. A vacuum-sealed cavity is typically susceptible to pressure increases due to gas generation during the hermetic sealing process and outgassing from the package material, sealing material, and components within the cavity. This pressure variation can degrade device performance and reduce device lifetime for many hermetically sealed microdevices. In addition, the packaging and/or equipment to provide an evacuated package can be complex and expensive.
It has been known to maintain a sealed vacuum within a cavity by using getters to adsorb vapor and gas species. Conventional gettering procedures have been met with varying degrees of success. For instance, with thick film getters there can be a reliability issue caused by getter particles falling down during fabrication process or after device experiencing vibration or shock due to poor mechanical strength and too large pore size of the used getter. The presence of separated getter particles has been identified as a major failure mode for some micro gyroscopes sealed with porous thick film getters. Additionally, because conventional getters typically have large pore size, the required size of the getter is normally large.
With relation to thin film getters, the mechanical properties of known amorphous or poly-crystalline silicon will change with deposition condition and are difficult to repeat. Known types of thin film getters are typically used in large sized cavities with large planar areas because of their limited thickness of only a couple of microns. It is, therefore, desirable to provide an improved microdevice and method of making a microdevice (such as a micro gyroscope) having a microstructure residing in a hermetically sealed cavity under a long term vacuum, that overcomes most, if not all, of the preceding problems.